How to check color image linear or nonlinear?

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anu 2017-2-13

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编辑： Image Analyst 2024-8-18，4:51

I have 24 bit RGB image. I want to check whether it is linear or nonlinear. How to check it.

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KSSV 2017-2-13

How a image can be linear and non linear? What you are expecting actually?

DGM 2024-8-17，22:26

I'm guessing that the question is how to determine whether an RGB image is sRGB or linear RGB.

That would probably be indicated in the file's metadata. I'm assuming that in the absence of any explicit specification the image is treated as sRGB, but I'm not certain of exceptions. If we knew what the format was, we might be able to eliminate some possibilities.

That said, there is no file or even a specified format, so we can't really narrow it down much more than that.

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Answer 1

Image Analyst 2024-8-18，4:44

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编辑：Image Analyst 2024-8-18，4:51

MacbethChartPamphlet.jpg

Image a gray scale step wedge with known reflectance percentages, like the Calibrite Color Checker Chart.

https://calibrite.com/us/product-category/photographers/?noredirect=en-US

Plot gray level vs. true, known reflectance value (see attachment) and see if it's a straight line going through the origin. It must go through the origin. If it's a straight line but does not go through the origin, then it's not linear.

Most digital cameras are not linear unless you specifically set the "gamma" to be 1. Some cameras (machine vision or scientific cameras) allow you to do that.

See this link for more information on camera linearization:

https://www.mathworks.com/help/images/end-to-end-implementation-of-digital-camera-processing-pipeline.html